Sealing arrangements such as labyrinth seals, carbon seals and mechanical face seals for controlling leakage from rotating equipment are known as are their advantages and disadvantages.
Labyrinth seals, for example, used in steam turbines are non-contacting and, therefore, have long life but their relatively high leakage rates require an auxiliary gland seal system. Such gland seal systems include highly complex and heavy seal regulators for reducing high pressure steam to the few pounds per square inch pressure required for gland sealing. Additional complexities and equipment involve several valves, high and low pressure drains, air ejectors and exhaust condenser as well as steam and air exhaust piping. The weight and space requirements of such system are high. For example, such support equipment in a typical ship's engine room has been estimated to weigh 3 tons.
Carbon ring seals, on the other hand, are contacting seals which tend to minimize steam leakage, but the contact between parts leads to relatively high wear rates.
Rotary gap type seals are also known such as that shown in U.S. Pat. No. 3,499,653 issued to Gardner, which teaches gas seals that are non-contacting at high speed and which control leakage by using hydrodynamic forces to control separation between sealing faces. At low speeds and/or pressures, however, some contact usually occurs resulting in wear and possible damage.
It is also known, as illustrated in U.S. Pat. Nos. 4,434,987 and 4,447,063, to use an electromagnet for controlling a gap between a rotating ring and a surrounding non-rotating ring in shaft seals wherein sealing fluid is pumped into the gap and exhausted through a bore in the stator elements. These devices also include an elastic bellows member for exerting an axial force on the non-rotating seal ring.
The object of the disclosed seal system is to overcome the limitations of the prior art systems by minimizing gas leakage, weight, space requirements and costs while increasing wear life.
Briefly stated, I have discovered that such objects may be obtained by the inclusion of one or more spring biased cylindrically shaped electromagnets disposed in stator elements on both sides of a rotating ring fixed to the shafts to be sealed. The gaps between the ring and the spring loaded magnets are boundary seals and may be closely controlled to maintain a small clearance completely around the circumference of the ring and the shaft on which it is mounted. Such an arrangement does not require elaborate sealing fluid pumping means and exhaust vents as used in the prior art. Moreover, the inclusion of rotor position sensing means, which will detect the distance between stator and rotor and hence the gap size, in combination with an electronic controller permits the boundary seal clearance to be dynamically controlled.
Still further, the arrangement allows the inclusion of a geometric labyrinth seal as a secondary sealing arrangement, thus increasing the safety factor of the disclosed shaft seal which is useful for controlling leakage from steam/gas turbines, compressors and other rotating equipment.